motors from accidental impact with a sheet of plastic or
even a layer of electrical tape.

If you’re thinking of moving from a Boe-Bot or other
small mobile robot platform to something based on the
Parallax wheel kit, take a moment to consider what’s
involved. You’re not simply replacing small, inexpensive,
lightweight servos with a heftier, more powerful (and
more expensive) drive system; you’ll have to upgrade your
entire development infrastructure.

For starters, you’ll have to stock up on heavy duty
aluminum stock — sheet metal, brackets, and fasteners. I’m
not talking about the solid chassis designs used to create
heavy-duty battle bots, but stock that’s significantly more
substantial than the easily workable aluminum and plastic
used with a typical carpet roamer.

Then there’s the issue of power. Forget about using a
AA battery pack. Instead, think 12V gell cell or — better
yet — a pair of six-cell, 7.2V NiMh battery packs sold for
R/C vehicles. I’ve had great results with the Dura Trax
six-cell, 7.2V, 4.2 Ah pack ($43 each) available from Tower
Hobbies (
www.towerhobbies.com). While you’re on the
Tower Hobbies website, pick up a few sets of two-pin Ultra
Plugs by W.S. Deans ($3/set). Try these quick connect, low
resistance plugs for your battery connections and you’ll
never want to use a Molex connector again.

Because of the mixed voltages required — 12 VDC for
the Parallax motors or HB- 25 motor controllers and 5V/3V
for the microcontroller and sensors — you should consider

a high-efficiency DC-DC converter. My favorite is
the programmable, three-channel RGi Power

Commander (($200), available from CrustCrawler

(
www.crustcrawler.com). I use it to convert the 14. 4
VDC from a pair of NiMh battery packs to 12V, 5V, and
3V, to power the motors, sensors, and Parallax Propeller
chip, respectively. Alternatively, you can use separate
battery packs and dedicated voltage regulators for each
voltage — but this wouldn’t be my first choice because of
the additional weight and space requirements.

You’ll also have to consider your tools. As noted
above, you won’t be working exclusively with easily
bendable aluminum, but you’ll have to learn to handle
heavy-duty stock. And this means you’ll probably have to
upgrade to heavy-duty tools — no more bending the
aluminum chassis with needle-nose pliers. Think bench
vise and rubber hammer.

Given the added expense of a medium-sized robot
over something that can fit in your hand, why make the
move? For one, you can create something practical — a
robot to fetch the paper, move a tray of food from one
room to another, or bring your medicines when they’re
prescribed, for example. You can also drop a laptop or
even a computer motherboard on a medium-sized platform
and have carrying capacity to spare. If you do decide to
make the move — with or without the Parallax motors —
drop me a line and a photo to share with your fellow
readers. SV

All peripherals are connected to an ATmega168
microcontroller running at 20 MHz, with free C-programming push-on/push-off
tools, libraries, and support for the Arduino environment. power button
reset
button